On Fri, Jan 09, 2026 at 04:11:23PM +0100, David Hildenbrand (Red Hat) wrote: > On 1/9/26 15:30, Zi Yan wrote: > > On 9 Jan 2026, at 8:26, David Hildenbrand (Red Hat) wrote: > > > > > On 1/9/26 14:19, David Hildenbrand (Red Hat) wrote: > > > > On 1/9/26 09:54, Francois Dugast wrote: > > > > > From: Matthew Brost <[email protected]> > > > > > > > > > > Add folio_split_unref helper which splits an unreferenced folio > > > > > > > > split_unref reads like "split and unref". > > > > > > > > You probably want to call this something like "folio_split_frozen" ? > > > > > > > > The very definition of "frozen" is "refcount = 0 ", so you can simplify > > > > the documentation. > > > > > > > > Are the folios you want to pass in there completely unused (-> free) or > > > > might they still be in use (e.g., migration entries point at them during > > > > folio split) > > > > > > > > So I am not sure yet if this should be "folio_split_frozen()" or > > > > "folio_split_freed()" or sth like that. > > > > > > > > I'm not CCed on the other patches in the series or the cover letter, so > > > > I don't see the context.
Here is a patchwork link to the entire series: https://patchwork.freedesktop.org/series/159119/ > > > > > > > > > > Ah, I was CCed on #3 where we call this function on folios that are > > > getting freed. > > > > > > In that case it would be acceptable to initialize folio->mapping (and > > > folio->index?) of the split folios. Do we also have to initialize > > > folio->flags, folio->private etc? > > > I lifted this code from FSDAX here: https://elixir.bootlin.com/linux/v6.18.4/source/fs/dax.c#L394 It seemly does everything we need for a zone_device split. > > > See __split_huge_page_tail(). > > > I'm not seeing this function defined anywhere. > > > folio_split_freed() would likely be best, because then it is clearer that > > > there is absolutely no state to copy from the large folio. > > > > Yes, basically, we do not have a reverse function of prep_compound_page() > > and > > open codes the reverse process in free_pages_prepare(). For zone devices, > > zone_device_page_init() calls prep_compound_page() to form a folio but > > free_zone_device_folio() never does the reverse. FS DAX has its own > > dax_folio_put() to do it. Alistair suggested to come up with a helper > > function for both FS DAX and free_zone_device_folio(). > > > > Maybe free_zone_device_folio_prepare() is better. And put it in > > mm/memremap.c. +1 can rename and move. > > That would be even better, if we can limit this completely to zone_device. Yes, I believe this function should only used by device private, device coherent, and fsdax folios which are all zone_device. I can add warning in this function too if it is called on non-zone_device folio too. Matt > -- > Cheers > > David
